Multi-scale thermal hydraulics calculations of FFTF "loss of flow without scram" transient with MATHYS
Résumé
During accidental transients such as the Loss Of Flow WithOut Scram (LOFWOS) in Sodium Fast Reactors (SFR), thermal hydraulics phenomena of various physical and temporal scales may occur, e.g. turbulent flow in the inter-wrapper gap, sodium mixing in large plena, fast power shut down and transition from forced to natural convection. Thermal hydraulics computational codes need to be able to model such phenomena using adequate models and optimized CPU time. This can be achieved thanks to multi-scale coupling: the most precise (but also CPU time-consuming) code is used only where it is necessary and is coupled with other faster codes.
IAEA’s international Coordinated Research Project (CRP) on the Fast Flux Test Facility (FFTF) sets a landmark for the validation of such codes by providing precious experimental data on a reactor scale. This paper presents CEA’s methodology and calculation using the MATHYS coupling code. This code uses the “overlapping domain” method to couple multiple scales and codes, namely CATHARE3 system
code, TrioMC subchannel code and TrioCFD CFD code. Inputs from other physics will be discussed and code to experiment comparison will be presented.